In the hospitality industry generally, and in hotels particularly, the ability to prepare spirit drinks, either mixed or straight, quickly and accurately is very important from a customer service point of view. Furthermore, in each State of Australia the sale of liquor is closely regulated by the Liquor Licensing Authorities and any establishment operating a bar service must comply with stringent requirements in relation to the dispensing of spirits and other liquors. In this connection, a standard shot of spirits in Australia is 30 milliliters, a half-shot is 15 milliliters and a double is 60 milliliters in volume. According to the Australian National Standards Commission any machine for the automatic dispensing of spirits must be sufficiently accurate to consistently dispense spirits with the following error margins:
15 ml .+-.0.6 ml PA1 30 ml .+-.1.0 ml PA1 60 ml .+-.1.5 ml. PA1 a metering reservoir having an air inlet, a liquor inlet and a liquor outlet provided therein, said air inlet being provided in an upper region of the reservoir and said liquor outlet being provided in a lower region of the reservoir wherein, in use, air supplied under pressure to the air inlet is used to force liquor to be discharged from the reservoir via said liquor outlet; PA1 a plurality of level sensors provided in the reservoir for sensing the level of liquor remaining in the reservoir, including a first sensor for sensing when the volume of liquor in the reservoir is at a first level, and a second sensor for sensing when the volume of liquor in the reservoir has fallen to a second level, wherein there is a predetermined difference in volume between the first and second levels; PA1 controller means for controlling the discharge of liquor via the liquor outlet in response to sensing signals from said first and second sensors respectively whereby, in use, an accurately metered quantity of alcoholic liquor is dispensed; and PA1 a first control valve connected to the air inlet for controlling the supply of compressed air to the reservoir in response to a control signal from said controller means, and wherein said first control valve is provided with an air outlet communicating with the air inlet of the reservoir, an air intake communicating with a source of compressed air and an air exhaust communicating with atmosphere, said first control valve having two modes of operation, namely a refilling mode in which air escaping from within the reservoir via said air inlet is directed to atmosphere via said air exhaust, and a discharge mode in which compressed air entering said air intake is directed into the reservoir via said air inlet.
Various types of automatic liquid dispensers are known in the prior art for dispensing a predetermined quantity of liquid. For example, WO 94/12427 discloses a liquid dispensing apparatus which employs a peristaltic pump for dispensing metered quantities of a liquid. A disadvantage of the apparatus of WO 94/12427 is the large number of moving parts and the consequent need for regular maintenance in view of the wear associated with the rotor and liquid transport lines of the peristaltic pump.
U.S. Pat. No. 5,316,181 discloses a liquid dispensing system having a liquid-filled reservoir, a controller microprocessor and a plurality of selectable outlets connected to the reservoir. A liquid level sensor provided within the reservoir is movable between a high position and a low position. The level sensor is used to provide an appropriate signal to the controller regarding the volume of liquid remaining in the reservoir. Metering of liquid from a selected outlet is controlled by the controller providing a signal to a selected valve at the end of a predetermined time period to close the valve. The time period together with the known rate of flow of liquid through the valve allows a specific amount of liquid to be dispensed. A difficulty with this method of metering liquid is that it requires an accurate measure and control of the flow rate of liquid through the system. This is only possible with expensive flow meters and/or complicated control systems.